The invention relates to an electrode for electrolytic processes, in particular to a cathode suitable for hydrogen evolution in an industrial electrolytic process. Reference will be made hereafter to chlor-alkali electrolysis as the typical industrial electrolytic process with hydrogen cathodic evolution, but the invention is not restricted to a specific application. In the electrolytic process industry, competitiveness is associated with different factors, the main of which being energy consumption reduction, directly connected with the process voltage; this justifies the many efforts directed to reduce it in its various components, for instance ohmic drops, which depend on process parameters such as temperature, electrolyte concentration and interelectrodic gap, as well as anodic and cathodic overvoltage. The problem of anodic overvoltage, in principle more critical, was tackled in the past by developing increasingly sophisticated catalytic anodes, based initially on graphite and later on titanium substrates coated with suitable catalysts, which in the case of chlor-alkali electrolysis are specifically directed to decrease chlorine evolution overvoltage. Conversely, cathodic overvoltage naturally obtainable with electrodes made of uncatalysed chemically resistant material (for example carbon steel) were accepted for a long time. The market is nevertheless demanding increasingly high caustic product concentrations, making the use of carbon steel cathodes unviable from a corrosion standpoint; furthermore, the increase in the cost of energy has made the employment of catalysts to be increasingly convenient also to facilitate cathodic hydrogen evolution. The most common solutions known in the art to obviate these needs are represented by the use of nickel substrates, chemically more resistant than carbon steel, and of catalytic materials based on ruthenium oxide or platinum. U.S. Pat. Nos. 4,465,580 and 4,238,311 for instance disclose nickel cathodes provided with a coating of ruthenium oxide mixed with nickel oxide, which for a long time has constituted a more expensive but technically better alternative to the carbon steel cathodes of the previous generation. Such cathodes however were affected by a rather limited lifetime, probably due to the poor adhesion of the coating to the substrate.
A substantial improvement in the adhesion of the catalytic coating on the nickel substrate was introduced by the cathode which comprises a nickel substrate activated with a platinum or other noble metal and a cerium compound, simultaneously or sequentially applied and thermally decomposed in order to obtain a catalytic coating based on platinum or other noble metal either diluted with cerium or, in a preferred embodiment, coated with a porous layer of cerium having a protective function: the role of cerium is in fact to destroy the possible iron-based impurities, which would prove harmful for the noble metal catalyst activity. Albeit an improvement over the prior art, the cathode presented a catalytic activity and a stability in electrolysis conditions not yet sufficient for the needs of present-day industrial processes; in particular, the coating tends to be seriously damaged by the occasional current inversions typically taking place in case of malfunctioning of the industrial plants.